240/120 Delta to 208y/120?

[chris kennedy]

Hello all, hope this finds you well.

I am being told the tranny bank below can't be rewired for 208y. Currently it is wired for 4 wire 240 delta. It would seem to me the primary to secondary winding ratio would allow the primary taps to be wired for either.

Please advise.

Thanks

http://i203.photobucket.com/albums/aa80/chris_kennedy/IMG_14101_zpso1ndpdli.jpg (http://s203.photobucket.com/user/chris_kennedy/media/IMG_14101_zpso1ndpdli.jpg.html)

[chris kennedy]

This is FPL BTW.

[lewy]

This bank can be changed from a 240 delta to a 120/208 wye. You would just have to parallel the secondary windings to make each transformer 120, or ground the x2 and turn each transformer back to 120/240 and just use 1 leg from each transformer, but you would only get half the KVA of each transformer.

[chris kennedy]

or ground the x2 and turn each transformer back to 120/240 and just use 1 leg from each transformer, but you would only get half the KVA of each transformer.

The tranny wouldn't like this set up would it? Unbalanced to the max.

[lewy]

The tranny wouldn't like this set up would it? Unbalanced to the max.
You asked if it can be rewired to 120/208 and the answer is yes it can. You would obviously have to change the connections and the customer would have some work to do, as far as unbalanced only if the customers load was unbalanced.

[chris kennedy]

You asked if it can be rewired to 120/208 and the answer is yes it can. You would obviously have to change the connections and the customer would have some work to do, as far as unbalanced only if the customers load was unbalanced.

Cool bet, thank you.

Would I still lose ½kva? My maths says if those trannys are 75's that would give me 100A 3Ø 208y/120

[lewy]

Depending on how you hook it up you either get 225KVA or 112

[Orgnizdlbr]

You asked if it can be rewired to 120/208 and the answer is yes it can. You would obviously have to change the connections and the customer would have some work to do, as far as unbalanced only if the customers load was unbalanced.

Yup, lewy is right on.....

[Lineman North Florida]

Take the lids off and split the pots, AC/BD leaving one bushing as you're dummy bushing, surely FP&L has a standard spec for which bushing is you're dummy bushing I would think, not real sure why someone would tell you that it could not be done unless there is something else that I'm not seeing.

[Rob]

Take the lids off and split the pots, AC/BD leaving one bushing as you're dummy bushing, surely FP&L has a standard spec for which bushing is you're dummy bushing I would think, not real sure why someone would tell you that it could not be done unless there is something else that I'm not seeing.

Yup..Most places it's X1. I like the White spool on the down guy!

[lewy]

Yup..Most places it's X1. I like the White spool on the down guy!
Ya I have never seen that before, we bring all of connections around the front.

[Orgnizdlbr]

That single spool on the down guy would be a big no no where I'm at.....

[reppy007]

That single spool on the down guy would be a big no no where I'm at.....

Im with you brother,a no no here too.Thats my climbing side if I had to replace a switch.Cant believe a guy would take the time to get the slack out of the guy just to install the spool when theres a better way :(

[Trouble1]

Always good to keep the keep the cut-outs right above the transformer, especially on three phase. Must be fun to move three times to open three doors too... Maybe that's why they are so close to the top of the cans. Open one and let the other two blow when the first one hits the top of the can. All the LA's up there too... Looks like a well constructed bomb. You guys must have the same people writing standards as where I work.:D

[Old Line Dog]

Yup..Most places it's X1. Yeah, I ran into that contractin. And finally got use to it. Personally... I always liked, and was raised with the X2 bushing left "Open". Just different "Growin up" places, right?? :-) :-)

[Lineman North Florida]

Yeah, I ran into that contractin. And finally got use to it. Personally... I always liked, and was raised with the X2 bushing left "Open". Just different "Growin up" places, right?? :-) :-) Left hand bushing or X3 on an additive pot is the dummy bushing where I'm at, but working different places I've seen any of the three be the dummy.

[Pootnaigle]

Umm I dont bleve that insulator is part of the down guy but I kinda think its there to help support that busswerk

[lewy]

We always put tape over the bushing that wasn't being used, not really sure why maybe just to let you know it wasn't being used. As far as the spool on the down guy to support the wire I agree with some of the others not something we would do. Finally as far as Cutouts over the bank only on a dead end otherwise on the other side of the pole, easier to operate as well as easier changing transformers if necessary.

[reppy007]

We always put tape over the bushing that wasn't being used, not really sure why maybe just to let you know it wasn't being used. As far as the spool on the down guy to support the wire I agree with some of the others not something we would do. Finally as far as Cutouts over the bank only on a dead end otherwise on the other side of the pole, easier to operate as well as easier changing transformers if necessary.

Thats funny,taping a bushing that isnt used...anybody can tell if a bushing isnt being used.Thats sort of like having a broken pole and floating the primary....so Ill just put tape around the pole so that others will know it isnt being used.....too funny !

[Orgnizdlbr]

Thats funny,taping a bushing that isnt used...anybody can tell if a bushing isnt being used.Thats sort of like having a broken pole and floating the primary....so Ill just put tape around the pole so that others will know it isnt being used.....too funny !

We ALWAYS tape the bushing that's not being used.

[Orgnizdlbr]

Umm I dont bleve that insulator is part of the down guy but I kinda think its there to help support that busswerk
Yeah Poot, it's there to hold the the buss tap, but take a good look, the guy goes through the hole in the single spool...... It ain't part of the guy it's just on the guy😳.

far as the cut outs go, we would mount them on the back arm away from the pots........

[reppy007]

We ALWAYS tape the bushing that's not being used.

OK...I just ever heard of that being done...so does that mean on urd,you would tape that bushing if it was not being used?Now you can laugh at me.....I have been known to use the smallest section of a yellow stick/pogo stick/extendo/scope stick....even guys here used to ask me why.....cause they didnt.....Im sure some guys here dont use it either.:) Its just that Im used to using it I guess.:(

[reppy007]

Maybe they should put a ladder against the pole,climb it and tape it,so that others will know it has no butt:D................http://abc13.com/weather/god-is-with-us-symbol-of-hope-found-in-tornado-debris/573573/

[Trouble1]

Just to add to the answers, you can't bank two banks together that have the dead bushing in a different place, even if they are the same voltage. Probably would never see it unless a contractor puts up a new bank on the system that is not aware of the standard.. maybe during a storm or something. Most here probably know it already, but it's good to know if you don't.

BTW, to the original poster, there is no such thing as 120/240 delta. You read 138 to ground with a digital meter, but there is no ground reference if working properly.

[lewy]

Just to add to the answers, you can't bank two banks together that have the dead bushing in a different place, even if they are the same voltage. Probably would never see it unless a contractor puts up a new bank on the system that is not aware of the standard.. maybe during a storm or something. Most here probably know it already, but it's good to know if you don't.

BTW, to the original poster, there is no such thing as 120/240 delta. You read 138 to ground with a digital meter, but there is no ground reference if working properly.
Could you clarify what you mean you can"t bank 2 transformers that have different dead bushings as I am sure you can bank them as long as you wire each transformer for 120. You are correct the bank would have to be either 120 or 240 delta, but not both.

[busman]

Just to add to the answers, you can't bank two banks together that have the dead bushing in a different place, even if they are the same voltage. Probably would never see it unless a contractor puts up a new bank on the system that is not aware of the standard.. maybe during a storm or something. Most here probably know it already, but it's good to know if you don't.

BTW, to the original poster, there is no such thing as 120/240 delta. You read 138 to ground with a digital meter, but there is no ground reference if working properly.

I assumed he meant this was a high-leg system. Three 240V transformers. One tranny center tapped and grounded. Gives you 120V to ground on A and C phases and 208V to ground on B phase. In the electrician world, the B phase has to be taped orange.

Mark

[Pootnaigle]

Umm my question is why wpould you wanna bank them 2 together? Thats kinda like restoring a chevrolet to look like a ford .Thems 2 seperate animals

[reppy007]

Umm my question is why wpould you wanna bank them 2 together? Thats kinda like restoring a chevrolet to look like a ford .Thems 2 seperate animals

Thats an easy question Poot....try some ole reppy :D

[chris kennedy]

I assumed he meant this was a high-leg system. Three 240V transformers. One tranny center tapped and grounded. Gives you 120V to ground on A and C phases and 208V to ground on B phase.

That is correct. High leg to C at the meter in linemans world.

[lewy]

A couple of different things here, yes with a 240 delta you can add a 120/240 service to 1 transformer, but this does not give you 120/208 3 phase like the OP was asking. Secondly as far as dead bushings in different locations, on an additive transformer the dead bushing would be on the left and on a subtractive transformer the dead bushing would be on the right and you could use both transformers in the same bank.

[Lineman North Florida]

A couple of different things here, yes with a 240 delta you can add a 120/240 service to 1 transformer, but this does not give you 120/208 3 phase like the OP was asking. Secondly as far as dead bushings in different locations, on an additive transformer the dead bushing would be on the left and on a subtractive transformer the dead bushing would be on the right and you could use both transformers in the same bank.
The dead bushing would be the one that the man who split the pot decided it would be X3 X2 or X1, they are split differently depending on where you go. As far as banking additive and subtractive pots together I agree it can be done, but on more than one occasion I have seen people who didn't realize that they had an additive and subtractive banked together in an open delta configuration and changed out the bad transformer which happened to be the subtractive pot with an additive, then built it back to company specs and after closing the bank in burnt up some stuff on the customers side, I realize that voltage should have been checked prior to leaving the call but in these 2 cases it apparently was not, we try to bank additives with additives and likewise with subtractives.

[reppy007]

The dead bushing would be the one that the man who split the pot decided it would be X3 X2 or X1, they are split differently depending on where you go. As far as banking additive and subtractive pots together I agree it can be done, but on more than one occasion I have seen people who didn't realize that they had an additive and subtractive banked together in an open delta configuration and changed out the bad transformer which happened to be the subtractive pot with an additive, then built it back to company specs and after closing the bank in burnt up some stuff on the customers side, I realize that voltage should have been checked prior to leaving the call but in these 2 cases it apparently was not, we try to bank additives with additives and likewise with subtractives.

It can be done,you would roll a highside or lowside.But I may have seen that done once if any.We,like you try to bank the same with the same.Although there was a time we banked 3 19.9 transformers.277/480.Two had two highside bushings and one had three.Took a bit to figure all that out but we did.That was years ago and by now I forgot all the details involved.....I just wanted to ask if anyone checks voltage on changed-out transformers before hooking up the secondaries,its a pain but Ive seen that done here.

[lewy]

The dead bushing would be the one that the man who split the pot decided it would be X3 X2 or X1, they are split differently depending on where you go. As far as banking additive and subtractive pots together I agree it can be done, but on more than one occasion I have seen people who didn't realize that they had an additive and subtractive banked together in an open delta configuration and changed out the bad transformer which happened to be the subtractive pot with an additive, then built it back to company specs and after closing the bank in burnt up some stuff on the customers side, I realize that voltage should have been checked prior to leaving the call but in these 2 cases it apparently was not, we try to bank additives with additives and likewise with subtractives.
I would think when splitting a pot for 120 phase to ground they would leave X2 as the ground, then it is just a matter of wether you use X1 or X3 as your live phase. We were always taught that H1 and X1 should have the same polarity so on an additive bank you would be using X1 on the right and on a subtractive bank you would be using X1 on the left, this is all assuming you are feeding the transformer on H1.

[Trouble1]

Sorry, made a vague statement and went away for a few days. I meant to say that you cannot bank two three phase banks of different polarities. Like if you wanted to upgrade one bank to a higher KVA, but not have the customer lose power, you could bank that bank to another bank the next pole of the same voltage for temp power if there happened to be one of the same voltage. I made a statement without really thinking it out, but you can possibly have the same polarity if the dummy bushings were in different spots on two different banks. Trying to point out that you could possibly change the polarity of the bank by moving bushings around. I don't know why you would but you could run into the scenario where a contractor that is from another part of the country put up a bank that is normal way for them, but not for you.

Just something to look out for.. banking banks is almost never worth the hassle though and we would just get a generator or do it at night Just thought I'd throw it out there in case someone came across it. Obviously an odd scenario, but you never know.

I have seen personally what happens when you bank two polarities together with step-downs... let's just say there is a lot of clean up.